Metallocene catalyst systems for olefin polymerization typically use an activator (also called a co-catalyst) to generate the active catalytic species. In general, there are two catalyst activator families: partially hydrolyzed aluminum alkyl complexes and non-coordinating anions (NCA's). Some of the more commonly employed partially hydrolyzed aluminum alkyl complexes include alumoxanes, such as methylalumoxane (MAO), for example. NCA-type activators are typically more active than their MAO counterparts, but are also quite costly and much more sensitive to poisons. NCA-type activators also cause problems with catalyst synthesis, handling, storage and reactor operation. MAO-based systems are more robust than their NCA-type counterparts, but MAO-based systems suffer from high costs of production, specifically, the large excess (relative to the amount of metallocene) of MAO used and its limited shelf life.
Alternative activators for metallocenes and other single-site polymerization catalysts have been the subject of numerous research efforts in recent years. For example, perfluorophenyl aluminum and borane complexes containing one anionic nitrogen-containing group have been studied. For example, R. E. Lapointe, G. R. Roof, K. A. Abboud, J. Klosin, J. Am. Chem. Soc. 2000, 122, 9560-9561, and WO 01/23442 A1 report the synthesis of (C6F5)3Al(imidazole)[Al(C6F5)3][HNR′R″]. In addition, G. Kehr, R. Frohlich, B Wibbeling, G. Erker, Chem. Eur. J. 2000, 6, No.2, 258-266 report the synthesis of (N-Pyrrolyl)B(C6F5)2. Supported activators for polymerization catalysts containing a Group 13 element and at least one halogenated, nitrogen-containing aromatic group ligand have also been reported. See, for example, U.S. Pat. No. 6,147,173 and U.S. Pat. No. 6,211,105.
U.S. Pat. No. 6,703,338 discloses teal treated indole modified silica used in combination with bis(1,3-methyl,butyl-cyclopentadienyl)zirconium dimethyl to polymerize ethylene, however does not disclose use of treated modified supports in combination with bis indenyl group 4 metallocene compounds to polymerize propylene to obtain good molecular weights at high yields.
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To enhance polymer morphology, metallocene polymerization catalysts operated in industrial slurry and gas phase processes are typically immobilized on a carrier or a support, such as alumina or silica. Metallocenes are supported to enhance the morphology of the forming polymeric particles such that the particles achieve a shape and density that improve reactor operability and ease of handling. However, the supported versions of metallocene polymerization catalysts tend to have lower activity as compared to homogeneous counterparts.
There is a need, therefore, for new, catalyst systems to polymerize propylene to good molecular weights at high catalyst yields, while preferably using lower catalyst loadings.